Vaccines against infectious disease have been hailed as the greatest achievement in public health over the last century. Despite the growing prevalence of severe fungal infections, no vaccines against fungi are in clinical trials or commercially available. We have engineered a live attenuated vaccine that protects against infection with the primary fungal pathogen Blastomyces dermatitidis. We and others have shown that vaccine immunity to this and other fungal infections is mediated by a dominant T1-cell response. In preliminary data, we found that T17 cells also are induced by vaccination and confer resistance against B. dermatitidis as well as related dimorphic fungi Coccidioides posadasii and Histoplasma capsulatum. In contrast to the prevailing dogma, we observed that T1 cells, but not T17 cells, are dispensable in this vaccine resistance and that T17 cells are also sufficient for the resistance. Vaccine-induced T17 cells mediated protection by recruiting and activating neutrophils and alveolar macrophages to the alveolar space to augment fungal killing. In this application, we propose to decipher the cellular receptors and innate signaling pathways that induce naive antigen-specific T-cells to differentiate into protective anti-fungal T17 cells. We have created a novel Blastomyces TCR transgenic mouse, which represents a key innovation that will let us analyze the requirements for differentiation of naive anti-fungal T-cells. We hypothesize that receptor recognition of Blastomyces mannans by the FcR3-Syk-Card9 and the TLR-Myd88 signaling pathways are essential to induce T17 cells and vaccine immunity. We also posit that Myd88-induced T17 differentiation involves pathway crosstalk between TLRs and Card9, and that TLRs collaborate with the mannose receptor to induce T17 cell differentiation. We provide strong preliminary data to support our hypotheses. Using our new Blastomyces-specific TCR Tg mouse, we have established an in vitro screen with bone marrow derived dendritic cells from knockout mice and an in vivo adoptive transfer system to delineate the signaling adaptors, pathogen recognition receptors, and fungal ligands that induce differentiation of naive antigen-specific CD4+ T- cells into protective T17 cells. Our approach offers a powerful complimentary strategy that will investigate the host receptors and signaling pathways in Aims 1 and 2, and the fungal ligands in Aim 3. Our work will provide new insight into the fungal pathogen recognition receptors and downstream signaling pathways, as well as the pathogen-associated molecular patterns that induce T17 cell differentiation. This knowledge will provide the fundamental basis for developing and designing new vaccine strategies against fungi, and will catalyze the discovery of novel adjuvants useful in vaccines against fungi and microbes in general. PUBLIC HEALTH RELEVANCE: The number of fungal infections has risen dramatically in the United States over the last 10 years, and is now in the top 10 in causes of death, partly because we lack vaccines against fungi. To address that public health need, we have generated an attenuated fungal vaccine, and an experimental model to study mechanisms of vaccine immunity to fungi. In this proposal, we will identify the host-pathogen interactions that are the foundation of vaccine-induced resistance. The knowledge gained from this research will lead to the development of fungal vaccines and adjuvants.